The present invention relates to a vehicle alternator having hook-shaped magnetic poles, and more particularly, the invention relates to an alternator for a vehicle in which leakage magnetic flux between the hook portions of the hook-shaped magnetic poles of the alternator is decreased by magnets.
In general, an alternator for a vehicle has a rotating yoke composed of a pair of hook-shaped magnetic poles arranged in facing relation to each other and forming a plurality of hook portions having N-poles and S-poles in the top ends thereof, magnetic-field windings to generate a magnetizing force in the hook-shaped poles wound inside the rotating yoke, and stator magnetic poles arranged in spaced relationship to form a certain gap with the rotating yoke. The magnetic flux put out from the hook portion of the hook-shaped magnetic pole of a N-pole returns to the hook portion of the hook-shaped magnetic pole of a S-pole through the stator magnetic pole to form a magnetic circuit. A stator winding is wound in the stator magnetic pole to generate an inductive electromotive force in the stator winding by intersecting the magnetic flux of the magnetic circuit with the stator winding, which forms an alternating generator.
In the alternator having such a construction, the magnetic flux intersecting with the stator winding produces the generated voltage according to the effective magnetic flux. However, there is some magnetic flux which is put out from the hook portion of the hook-shaped magnetic pole, but does not enter into the stator magnetic pole due to leakage. In order to improve the efficiency of generation, it is necessary to decrease the leakage magnetic flux.
In a conventional alternator for a vehicle, various ways of decreasing leakage magnetic flux between hook portions of hook-shaped magnetic poles are described in (1) Japanese Patent Application Laid-Open No. 54-116610 (1979), (2) Japanese Patent Application Laid-Open No. 61-85045 (1986), (3) Japanese Patent Application Laid-Open No. 3-251067 (1991), (4) Japanese Patent Application Laid-Open No. 2-159950 (1990).
The above-referenced publication (1) calls for an adhesive containing a hard magnetic material to be filled between the hook portions of hook-shaped magnetic poles; the above-referenced publications (2) and (3) call for magnets to be arranged between the hook portions of hook-shaped magnetic poles, and the above-referenced publication (4) calls for magnets to be arranged on the outer peripheral surface of the hook portions of hook-shaped magnetic poles.
The arranging of magnets between the hook portions of hook-shaped magnetic poles to prevent the magnet from fracturing and scattering due to centrifugal force during high speed rotation is described in (5) Japanese Patent Application Laid-Open No. 4-251553 (1992), (6) Japanese Patent Application Laid-Open No. 3-265450 (1990) and (7) Japanese Patent Application Laid-Open No. 5-207716 (1993).
The above-referenced publication (5) calls for a non-magnetic material member, such as metal tension tape, to be arranged cylindrically in the outer periphery of the magnets and the hook portions of hook-shaped magnetic poles; and the above-referenced publication (6) and (7) calls for a non-magnetic material ring having projections and depressions in the radial direction attachable to the end surfaces and the peripheral surfaces of the hook portions of the hook-shaped magnetic poles to be arranged in the outer periphery of the magnets in such a way as to be even with the outer peripheral surface of the hook portions of the hook-shaped magnetic poles.
However, these proposals have the following disadvantages.
There arises a problem in that the fillers of the adhesive containing hard magnetic material in the case of the above referenced publication (1) and the magnets in the cases of the above conventional technologies (2) to (4) are fractured and scattered due to centrifugal force during high speed rotation.
In the proposals described the above referenced publications (5) to (7), the above problem can be solved by arranging a bursting-out protector, such as metal tension tape or a non-magnetic material ring, in the outer periphery of the magnets. However, in the conventional technology (5), there arises a problem in that the magnetic resistance between the hook portion of the hook-shaped magnetic pole and the stator magnetic pole is increased so that the effective magnetic flux decreases, and consequently the efficiency of generation decreases since the gap between the hook portion of the hook-shaped magnetic pole and the stator magnetic pole increases by the thickness of the bursting-out protector.
In the proposals described in the above-referenced publications (6) and (7), there arises a problem in that the effective magnetic flux decreases as the leakage magnetic flux decreases so that small size magnets cannot help to be used, and consequently the efficiency of generation decreases since the magnets are arranged in a non-magnetic material ring having bumps and dips.
Further, in the proposals described in the above-referenced publications (5) to (7), there arises a problem in that the hook portions of the hook-shaped magnetic poles are lifted up due to centrifugal force during high speed rotation.